Direct boot from NVME disk is possible only if you have SPI flash with bootloader. If you don’t have it, boot loader must be on eMMC. If you don’t have eMMC, bootloader must be on SD card. Tool nand-sata-install moves a content of SD/eMMC to NVME driver and adjust boot process that your system loads from NvME. But boot loader remains on eMMC. If you remove it, you will not be able to boot from NvME …
If you do have (updated!) SPI flash, this is enough:
I see. There is a lot of complications to update u-boot on SPI … Perhaps do the update part by using Radxa Debian. Search also this forum. I think I saw a quicker solution.
IMO This is the only package you need to install, once you add Radxa repository.
apt-get install -y rockpi4b-rk-u-boot-latest